Supplementing with formula

My daughter is about 11 weeks old. I am going back to work soon so I wanted to start supplementing her with formula. Should I start with Similac Advance or Sensitive. She is still spitting up and only having a bowel movement every few days. How should I do it? Mixing BM and formula or just switch a feeding with formula only? Also she had bloody stool with the vitamin D supplement. Is there formula without vitamin D? Thank you.

You should be able to start with either the Similac Advanced or Similac Sensitive. I’d recommend you start with Similac Advanced. The commercial infant formulas that I am aware of all contain vitamin D, but so does your breast milk. I doubt she has a sensitivity to vitamin D itself, but more like something else in the vitamin D supplement. After all she has tolerated your breast milk for almost 3 months.

As far a spitting up goes - Mild spitting up without force or pain in a child growing well sounds normal. More on GERD / spitting up . If you are worried about her spitting up you could try a pre-thicken formula like Similac spit up or Enfamil AR, but I doubt that is needed.

Her stooling pattern also sounds normal. Soft, non-bloody stools every other day is within normal limits. More on bowel movements in children

Lastly, the issue of how to start formula feedings. You are probably fine mixing formula with breast milk but there is no known advantage. Mixing does not help infants “adjust” to formula. In our home, our baby gets both breast milk and Similac Advanced secondary to poor milk supply. We regard breast milk as “liquid gold” and choose to feed it first and then finish the feeding with formula.

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